Tape recording and reproducing systems for use as computer data storage devices are required to provide high data transfer rates and to perform a read check on all written data. To satisfy these requirements, conventional tape systems employ various methods of recording, including linear recording, in which the tracks of data lie parallel to each other and to the edge of the tape and helical scan recording, in which the tracks of data lie parallel to each other but at an angle to the edge of the tape. The linear recording method offers higher data transfer rates; however, it is desirable to obtain higher data densities while retaining the advantages of this method.
Tape track densities are limited by crosstalk, which occurs when reading is interfered with by data of adjacent tracks. Crosstalk is exacerbated by error in head gap alignments.
A method of recording known as azimuth recording has been shown to decrease the effects of crosstalk and thus increase the track density of tape recording systems. Azimuth recording results in a recorded track pattern in which the magnetization directions of adjacent data tracks lie at different azimuth angles relative to each other. This method greatly reduces intertrack crosstalk, enabling tracks to be placed closer together.
A typical recorded track pattern resulting from the use of a tape recording system utilizing azimuth recording is shown in FIG. 1. The tracks 7 and 9 are recorded such that the direction of magnetization of the data is at a first angle-theta relative the lateral direction of the tape 50. Tracks 6 and 8 are recorded at a second such angle+theta.
The azimuth recording shown in FIG. 1 is achieved through utilization of a typical magnetic head like the one shown in FIG. 1a. Referring to FIG. 1a, the face 61 of the magnetic head 60 contains a first column 62 of write head gaps 72 and 73, a second column 66 of write head gaps 76 and 77, and a third column 64 of read head gaps 74 and 75 situated between the columns 62 and 66. The head gaps of each column are arranged such that their lengths extend in a lengthwise or longitudinal direction generally parallel to the direction of arrow 71, as shown in FIG. 1a. The write head gaps 72 and 73, the write head gaps 76 and 77, and the read head gaps 74 and 75 are typically arranged such that there is an end-to-end space 63 between them. Further, the corresponding head gaps in columns 62 and 66 are positioned such that the write head gaps 72 and 76 are generally laterally aligned. The read head gaps 74 and 75 in the third column 64 are offset in a lengthwise direction and distance 65 from the corresponding write head gaps in the other two columns 62 and 66. In this arrangement, magnetic head 60 enables azimuth recording of multiple tracks at once.
As shown in FIG. 1b, magnetic head 60 is typically mounted on head assembly 100, as shown in dashed lines in FIG. 1b, for lateral and stepped rotatable movement relative to a tape such as that shown in FIG. 1. As shown, the magnetic head 60 is mounted for movement about the output shaft of a rotary motor 106. The rotary motor 106, which receives input from a controller 200, serves to rotatably step the angle of magnetic head 60 relative to the tape 50. A stepper motor 108, which also receives signals from the controller 200, serves to engage an actuator 107, shown as a linear actuator in FIG. 1b, for moving the magnetic head 60 in a lateral or widthwise direction across the tape 50.
Referring to FIG. 1c, during operation of a typical azimuth recording system, the magnetic tape 50 moves in a direction indicated by the arrow 79 over the magnetic head 60. As shown on the right side of FIG. 1c, the magnetic head 60 is rotated in a positive angle relative to tape 50, denoted by +theta, bringing the write and read head gap pairs 72 and 74, and 73 and 75, into general alignment with tracks 52 and 54, respectively. Write head gaps 72 and 73 write tracks 54 and 52, respectively, on tape 50. These tracks extend generally parallel to the edge of tape 50. In this way tracks are recorded in which the magnetization direction of the data is at a positive azimuth angle on the tape 50.
Referring to FIGS. 1c, when the end of the tape 50 is reached, the direction of travel of the tape 50 is reversed to advance the tape 50 in the direction indicated by the arrow 78. Stepper motor 108 activates linear actuator 107 which moves the magnetic head 60 laterally over the tape 50 to the next track position to be written. The rotary motor 106 rotatably steps the magnetic head 60 to a negative angle, denoted by -theta as shown on the left side of FIG. 1b. This brings the read and write head gap pairs 74 and 76, and 75 and 77, into general alignment with the tracks 55 and 53, respectively. In this position, the write head gaps 76 and 77 write the tracks 55 and 53, respectively, which extend parallel to the edge of the tape 50. These tracks are written at a negative azimuth angle. And again, due to the azimuth position, -theta, of the magnetic head 60, the read head gaps 74 and 75 are able to read check all data written by write head gaps 76 and 77 respectively.
Conventional tape recording systems have employed various azimuth adjustment mechanisms. One such mechanism is disclosed in U.S. Pat. No. 4,539,615 to Arai et al. entitled, "AZIMUTHAL MAGNETIC RECORDING AND REPRODUCING APPARATUS" which describes a stepping motor and a gear box to rotate the magnetic head into the desired azimuth angle. The disadvantages of this type of mechanism, are the physical size of the gear box and the number of gears required to achieve the high gear ratios necessary for high track density recording and reproducing. The gear box decreases the efficiency and lowers the bandwidth of the mechanism, which impedes the performance of the mechanism. Furthermore, the backlash from multiple sets of gears in the gear box will induce inaccuracies in the positioning of the tracks making high track densities difficult to achieve. Backlash is created by the loss of contact between gears during changes of rotational direction. During starting and reversing of gears, backlash creates inaccuracy, particularly in a gear box, wherein backlash has a cumulative effect from each gear. Bandwidth measures the speed with which gears can change directions of rotation. Generally, smaller gears and lesser number of gears perform at higher bandwidths and are thus more desired.
As tape recording systems become increasingly smaller and the track density becomes increasingly greater, the need to limit the physical size and backlash as well as the need to increase bandwidth of head actuation mechanisms becomes critical.
In any method of tape recording, it is highly essential to position the magnetic head such that the face of the head exhibits a zero zenith, i.e. the face of the head is substantially parallel relative to the plane of the tape path. Zero zenith enables the different read/write channels of the head to make uniform and consistent contact with the tape, which enables uniformly strong signals to be read and written. In addition, the different read/write channels of the head will remain in uniform contact with the tape as the head moves up and down along the transverse direction of the tape to read and write different tracks.
In the prior art, proper zenith of the head was achieved by tightly controlling all the mounting surfaces to very tight tolerances. For example, FIG. 2 shows a tape guide system 3 and a vertically moveable platform 2 on which a read/write head 1 is mounted. The platform 2 is first aligned parallel to datum A of the baseplate. The tape guide system 3 is then aligned perpendicular to datum A. The read/write head 1 is then aligned perpendicular to its mounting surface 5 which is mounted onto platform 2. Thus when all three components are aligned, the zenith may still be off by as much as the sum of all the allowable tolerances in the alignment of the three components.
Alternatively, another method of achieving proper zenith in the prior art was to adhesively attach the magnetic head in place after aligning the zenith using gages. The disadvantages of this method are that zenith may still be misaligned once the adhesive shrinks during curing and the amount of time required for this type of process.
Thus, a hitherto unsolved need has remained for a magnetic head tilting mechanism which combines the functions of azimuth and zenith adjustment in a cooperative, synergistic manner and to reduce overall head assembly components count, size, and overall complexity.